Shaft for golf club

ABSTRACT

There is provided a golf club shaft in which the shaft is properly flexed at the time of swing and an excessive deformation of the shaft is restricted at the time of impact, a high repelling force is generated, and thereby an initial speed of the ball and the carry of the ball are further improved and which is quite suitable for using a club head having a low center of gravity or a large sized club head. This golf club shaft is filled with the resilient material having a feature in which a rapid application of force against the entire inner part of the hollow shaft or its extremity end causes a high repelling force to be acted on to cause it to be hardly deformed and in turn a gradual application of force causes itself to be easily deformed.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation application of U.S. patentapplication Ser. No. 09/569,247, filed May 11, 2000, and which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a golf club shaft.

[0004] 2. Description of the Related Art

[0005] A usual gold club is made such that its shaft is formed into ahollow shaft under application of high strength high resilient fiber(for example, a carbon fiber) so as to reduce its entire weight, whereinan initial speed of a golf ball and a carry of the golf ball areimproved by increasing a head speed due to a deformation (bending) ofraw material of the golf club during its swing and increasing arepelling force generated when the deformed shaft is recovered to itsoriginal shape. In addition, as a trend of the recent golf club, theclub head is made to have a large size and a setting of low center ofgravity, the shaft is changed into a long and soft shaft and then thehead speed and the repelling force are increased to improve the initialspeed of the ball as well as its carry.

[0006] In addition to the aforesaid head speed or the repelling force,as a factor for increasing the carry, it is known in the art that theinitial speed of the ball is improved more effectively to extend thecarry by striking the ball 103 at an upper location than a crossingpoint of a perpendicular suspended from the center of gravity 101 of theclub head 100 as shown in FIG. 9.

[0007] This is a so-called vertical gear effect, wherein acounter-clockwise couple 105 is generated at the club head 100 due toshock in a direction of an arrow 104 generated when the ball 103 strikesagainst the club head 100 advancing forward in the direction of arrow102 at the time of impact and then this couple 104 causes the shaft 106to be crushed in a direction of an arrow 107.

[0008] That is, a relation between the couple 105 of the club head 100and a deformation of the shaft 106 causes the ball 103 to be rotated ina clockwise direction, resulting in that a back-spin influencing againsta carry is reduced and a striking angle is increased, and nowadays thereis provided a countermeasure in which a size of the club head 100 isincreased in a vertical direction and concurrently a low center ofgravity of the club head is set.

[0009] However, as a result in which the low center of gravity or largesize setting of the club head 100 described above was promoted, adeformation of the shaft 106 caused by the couple 105 at the time ofimpact was excessively increased as shown in FIG. 8 and also the loss ofenergy caused by deformation of the shaft 106 was excessively increased,resulting in that there was a certain limitation in increasing theinitial speed of the ball.

[0010] The present invention has been invented in view of the aforesaidcircumstances in the prior art and it is an object of the presentinvention to provide a golf club shaft in which the shaft is properlyflexed at the time of swing, an excessive deformation of the shaft isrestricted at the time of impact, the initial speed of the ball isimproved while a high repelling force is being generated, thereby acarry is further improved and the shaft is quite suitable forapplication of the club head having a low center of gravity or a largesize.

SUMMARY OF THE INVENTION

[0011] The present invention has employed the following technical meansin order to accomplish the aforesaid object.

[0012] In accordance with the technical means in first aspect, there isprovided a golf club shaft in which the entire inner region of thehollow shaft is filled with resilient material having a feature in whicha rapid application of force causes a high repelling force to be actedon it to be hardly deformed and in turn a gradual application of forcecauses the shaft to be easily deformed.

[0013] In accordance with the technical means described in first aspect,the resilient material filled in the shaft may act on deformation of theshaft.

[0014] That is, since the gradual application of the force is applied tothe shaft at the time of swing, the filled resilient material may easilybe deformed to assure a flexing of the shaft when the shaft is swung. Inaddition, at the time of impact, a rapid application of the force isapplied to the shaft by a shock where the ball strikes against the clubhead, so that a high repelling force is generated at the filledresilient material to cause it to be hardly deformed and in turn therepelling force of the resilient material may act as a repelling forcefor the shaft at the time of impact and concurrently a deformation ofthe shaft is restricted by the repelling force to reduce an energy lossgenerated at the time of impact.

[0015] Although the technical means described in first aspect as aboveis set such that the resilient material is filled in the entire shaft,this is not limited to this constitution but it may be filled at thepart of the shaft.

[0016] For example, as disclosed in the technical means described insecond aspect, there is provided a golf club shaft filled with resilientmaterial having a feature in which if a rapid application of the forceat the inner extremity end of the inner shaft causes a high repellingforce to be acted on it to cause it to be hardly deformed and in turn ifa gradual application of force at the inner extremity end of the innershaft causes the material to be easily deformed.

[0017] That is, the extremity end portion of the shaft is a part wherethe deformation caused by a couple at the time of impact may easily beproduced and also mostly influence a carry of the ball as well as itscharacteristic of flying direction, resulting in that filling of theresilient material in the shaft may cause the same action as that offirst aspect.

[0018] As a practical range of the extremity end, it is preferable thatthe range of the extremity end where the resilient material is filled isfrom 30 cm to 40 cm from the neck end or from near the end part asdisclosed in the technical means in third aspect.

[0019] In the foregoing description, although both restriction againstthe excessive deformation of the shaft and assuring of the repellingforce of it are assured only with the resilient material, it may also beapplicable that a core rod is stored within the shaft along its axis,the lower end of the core rod is fixed to the extremity end of the shaftand at the same time the core rod is inserted into the resilientmaterial to assure restriction of excessive deformation of the shaft aswell as repelling force as disclosed in the technical means of fourthaspect.

[0020] In accordance with the technical means of fourth aspect, arepelling force from the deformation where the resilient material iscrushed with the core rod from inside is added to the repelling forceattained from the deformation caused by the deformation of the shaft atthe time of impact of the resilient material. That is, the repellingforce of the resilient material may act against both shaft and core rod,resulting in that both restriction of the excessive deformation of theshaft and assuring of the high repelling force can be carried out moreeffectively.

[0021] Further, as described in the technical means of fifth aspect, thefixed state of the core rod and the resilient material through adhesionenables both restriction against the excessive deformation of the shaftand assuring of the high repelling to be carried out more effectivelyand further a certain deformation of the core rod is produced bydeformation of the shaft, although the resilient material integrallyassembled with the core rod is deformed in concurrent with the core rod,so that the repelling force of the resilient material can be transmittedto both shaft and core rod without producing any time loss.

[0022] In addition, the resilient material may be adhered or fixed tothe shaft as disclosed in the technical means of sixth aspect and inaccordance with this feature, the repelling force of the resilientmaterial may act against a twisting of the shaft to cause the shaft tobe hardly twisted and so this is effective in view of improving itsdirection-oriented feature.

[0023] The resilient material is not limited to one in which its entirematerial is adhered and fixed to the shaft, but its part is adhered andfixed to the shaft, wherein as disclosed in the technical means ofseventh aspect, for example, it can be applied that the upper end of theresilient material is adhered to and fixed to the shaft, and as thisconstitution, an assembly in which the resilient material is filled atthe extremity end of the shaft as disclosed in second and third aspectsis preferable.

[0024] As the resilient material in the present invention, it includesall the materials having such a feature as one in which a rapidapplication of the force causes a high repelling force to be acted andcauses the material to be hardly deformed and in turn a gradualapplication of the force causes the repelling force to be weakened andcauses the material to be easily deformed and more practically it ispreferable to apply the resilient material of high molecular system.

[0025] Further, more practically, following resilient materials can beapplied.

[0026] For example, they are polyurethane (foam under mixture ofpolyisocyanate and polyol), polyethylene (foam), polystylene (foam),latex foam, foamed rubber, pouncing putty (immersed with siloxanecontaining boron atom), and further butadiene-acrylonitrile copolymer,chloroprene polymer, ethylene propylene copolymer, acryl copolymer,stylene-butadiene copolymer, isobutylene-isoprene, polybutadiene,natural polyisoprene, synthetic polyisoprene, natural rubber, rubbers ofpolyvinyl chloride, rubbers of polyamide, polyvinyl copolymer,polyolefins, synthetic rubber, propylene, nitrele, isoprene, silicone,uria, phenol, foams selected from these substances or mixed with thesesubstances.

[0027] The shaft of the present invention is constructed such that theresilient material may easily be deformed at the time of swing, so thatit is satisfactory if the resilient raw material substantially deformedat the time of swing is used to increase the head speed at the time ofswing and further it is the most applicable case that the resilient rawmaterial of as soft as possible and in particular it is satisfactorythat the material is used at the extremity end of the shaft.

[0028] Additionally, the method for filling the resilient material inthe shaft is optional and as its example, the resilient material isformed into the shape corresponding to the inner portion of the shaftand inserted into the shaft. In the case of the club shaft in which thecore rod is provided, the resilient material may be inserted into theshaft under a state in which the resilient material is being fixed tothe core rod or the resilient material formed into the shapecorresponding to the inner portion of the shaft may be inserted afterthe core rod is fixed to the shaft.

[0029] In order to make an inserted state of the core rod and theresilient material, it is possible to insert the core rod into theresilient material or wind the resilient material around the core rod orto perform a direct foaming within the shaft.

[0030] In Table 1 (the prior art product) and Table 2 (the presentinvention) are indicated the results in which the initial speed of theball and the carry of the ball in the golf club where the prior artshaft and the shaft of the present invention were used were measured bythe following methods.

[0031] Measuring method: A ball is hit in a specified swing speed (50m/s) by a golf club swing mechanism made by Miyamae Co., Ltd. an initialspeed (m/s) of the ball is measured by a trajectory measuring machinemade by Bridgestone Sports Co., Ltd. and a flying distance (carry) ismeasured by a computer simulation in reference to the speed.

[0032] Configuration of the Applied Clubs:

[0033] Shafts: Both prior art product and the product of the presentinvention:

[0034] Full length of 1143 mm and weight of 55 g made of similar carbonfiber having the same number of plies

[0035] Club Head:

[0036] Both prior art product and the product of the present inventionhave a loft angle of 10.5°, a lie angle of 55° and a weight of 193 g

[0037] The resilient material (only the product of the presentinvention):

[0038] Raw material: foamed polyurethane

[0039] Density: 0.3 (g/cm³)

[0040] Asca C hardness: 33

[0041] Repellent resiliency: 50 (%)

[0042] Compressive residual strain: 4 (%)

[0043] Amount of use: 30 cm at the extremity end TABLE 1 1 2 3 4 5 6 7 89 10 AV Head 50 50 50 50 50 50 50 50 50 50 50 Speed Ball 67 66 65 64 6463 63 65 64 65 65 Speed Carry 226 225 218 207 221 205 216 225 221 222219

[0044] TABLE 2 1 2 3 4 5 6 7 8 9 10 AV Head 50 50 50 50 50 50 50 50 5050 50 Speed Ball 69 68 68 69 68 68 68 67 68 67 68 Speed Carry 247 237245 241 247 246 247 234 242 242 243

[0045] In view of the result of measurement described above, it has beenproved that the product of the present invention exceeded as comparedwith that of the prior art in reference to the ball speed by a maximumvalue of 6 m/s and an average value of 3 m/s and the constitution of thepresent invention was quite effective for improving the initial speed ofthe ball. In addition, as to the carry, the present invention wassubstantially improved over the product of the prior art by the maximumvalue of 42 m and the average value of 24 m.

EFFECTS OF THE INVENTION

[0046] As proved in reference to the aforesaid result of measurement,the present invention can provide a golf club shaft having the initialball speed and the carry quite improved by filling the resilientmaterial having a characteristic in which it is hardly deformed under anaction of the high repelling force upon rapid applying of force to theinner side of the shaft and in turn it is easily deformed upon gradualapplication of the force.

[0047] In addition, both restriction over the excessive deformation ofthe shaft and assurance of the repelling force can be carried out moreeffectively by the inventions described in fourth and fifth aspects, sothat it can be expected to have more improved initial speed of the balland the carry.

[0048] Additionally, since the resilient material can be acted againstthe deformation of the shaft in a twisting direction by the inventionsof sixth and seventh aspects, this is quite effective for stabilizingthe directional characteristic of the ball, resulting in that thepresent invention becomes the golf club shaft in which not only theinitial speed of the ball and its carry can be improved but also it hasa quite superior directional characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049]FIG. 1 is an elevational view with a part being broken away toshow a substantial part of a golf club in which the golf club shaft ofthe present invention is used.

[0050]FIG. 2 is an enlarged sectional view taken along line II-II ofFIG. 1.

[0051]FIG. 3 is an operational view for showing a deformation state ofthe shaft ranging from its down-swing state to its impact state.

[0052]FIG. 4 is a side elevational view with a substantial part beingbroken away for showing a deformation state of the shaft at the instanttime of impact.

[0053]FIG. 5 is a side elevational view with a part being broken away toshow a substantial part of the golf club in which the golf club shaft ofanother preferred embodiment of the present invention is used.

[0054]FIG. 6 is an enlarged sectional view taken along line II-II ofFIG. 5.

[0055]FIG. 7 is a side elevational view with a substantial part beingbroken away to show a state of deformation at the instant time of impactin the shaft shown in FIG. 5.

[0056]FIG. 8 is an operational view for showing a state of deformationin the prior art shaft ranging from its down-swing to its impact.

[0057]FIG. 9 is a side elevational view for showing a state ofdeformation of the prior art shaft at the instant time of impact.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Referring now to the drawings, some preferred embodiments of thepresent invention will be described as follows, wherein FIGS. 1 and 2illustrate a golf club A which the golf club shaft 1 of the presentinvention is used. At first, the constitution of the golf club A will bedescribed.

[0059] The shaft 1 is of a hollow structure in which a plain sheet ofhigh strength high resilient fiber (for example, carbon fiber) immersedwith synthetic resin or high strength high resilient filaments immersedwith synthetic resin is wound. Since this structure is of a well-knownstructure, its detailed description will be eliminated.

[0060] Reference numeral 2 denotes a club head, wherein the well-knownraw material (for example, titanium) is formed into a predeterminedshape and the shaft 1 is inserted and fixed to the neck part 3integrally arranged at its upper surface.

[0061] Reference numeral 4 denotes a resilient material which is filledin the shaft 1 within a range of 30 cm from the upper end 31 of the neckpart 3 toward the upper part of the shaft 1, its upper part is adheredto and fixed to the inner surface of the shaft with adhesive agent 5over its entire circumference.

[0062] The resilient material 4 is of high-molecular system having acharacteristic in which a high repelling force may act on it upon rapidapplying of force to cause it to be hardly deformed and in turn agradual application of the force to it causes the repelling force to beweakened and easily deformed.

[0063] Incidentally, one example of the method for filling the resilientmaterial 4 will be described, wherein the resilient material 4 has itsouter diameter formed to be larger than an inner diameter of the shaft 1at a location where the resilient material 4 is filled and after theadhesive agent is coated at the predetermined position, the material ispushed into the shaft at the upper end side or the lower end side (notshown) of the shaft 1 and filled there. As to the filling method, thisis not limited to the aforesaid method, but it is also optional toperform it with another method.

[0064] Referring now to FIGS. 3 and 4, the state of deformation of aseries of shafts 1 when a ball 6 is hit by the golf club A constitutedas described above will be described.

[0065] At first, at the time of down-swing, the resilient material iseasily deformed, so that the shaft 1 is properly flexed and this flexingstate may increase the head speed.

[0066] Next, at the time of impact, a couple D is generated at the clubhead 2 by the shock in the arrow direction C2 when the ball 6 strikesagainst the club head 2 advancing forward in the arrow direction C1 asshown in FIG. 4 and then the couple D deforms the shaft 1 to crush itfrom the arrow direction E.

[0067] A period of time when the shaft 1 is deformed at the time ofimpact is faster than that when the shaft 1 is flexed at the time ofdown-swing by about 100 to 1000 times, i.e. at the time of impact, aforce is rapidly applied as compared with the time of down-swing inwhich a gradual application of force is applied.

[0068] At this time, the filled resilient material 4 is compressed asthe shaft 1 is tried to deform and a high repelling force is generatedby this compression and then this repelling force restricts thedeformation caused by the impact of the shaft 1 to a minimum state andconcurrently this repelling force restricts a vibration of the shaft 1.That is, an energy loss at the time of impact is reduced and thereby arepelling force of the shaft at the time of impact is concentratedagainst the ball 6, so that an improvement of the initial speed of theball and the carry of it is realized.

[0069] In addition, since the resilient material 4 is adhered to theshaft 1, a repelling force may act on the shaft 1 against deformation ina twisting direction of it, so that a stable direction of it is alsorealized.

[0070]FIGS. 5 and 6 show a golf club A1 in which a shaft of anotherexample in the preferred embodiment of the present invention is used.The same portions as those of the aforesaid example are denoted by thesame reference numerals and their description will be eliminated.

[0071] The golf club A1 of the preferred embodiment is provided with acore rod 7 fixed inside the shaft 1 and passing through the resilientmaterial.

[0072] The core rod 7 is formed by a core rod 71 made of raw materialwhich is at least harder than the resilient material and has such atension as one capable of compressing the resilient material (forexample, metal, carbon fiber, glass fiber and hard synthetic resin andthe like) and the same length as the entire length of the resilientmaterial 4; and a fixing part 72 at the rear end of the core rod havingthe same length as the entire length of the neck part 3.

[0073] The core rod 71 is formed into a fine rod shape and passesthrough the resilient material 4 along an axis of the shaft 1. Thefixing part 72 is formed to have an outer diameter approximately adaptedfor an inner diameter of the shaft 1 corresponding to the neck part 3,adhered and fixed with adhesive agent 51.

[0074] Incidentally, one example of the method for filling the resilientmaterial 4 in the preferred embodiment will be described, wherein theouter diameter of the resilient material 4 is formed to be larger thanan inner diameter of the shaft 1 where the resilient material 4 isfilled and a through-pass hole 41 through which the core rod 71 may passis opened along its axial line. Then, the core rod 7 is inserted at thelower end of it into the through-pass hole 41 and fixed there andadhesive agent is coated at the predetermined positions of the resilientmaterial 4 and the fixed part 72, thereafter it is pushed at the upperend side or the lower end side (not shown) of the shaft 1 and filled.The filling method is not limited to the aforesaid method, but othermethods are optionally available.

[0075] Then, referring to FIGS. 3 and 7, a deformation state of theshaft 1 when the ball 6 is hit by the golf club A1 constituted as abovewill be described as follows.

[0076] At first, at the time of down-swing, the resilient material 4 iseasily deformed in the same manner as that of the aforesaid example, sothat the shaft 1 is properly flexed and this flexing increase the headspeed.

[0077] Then, at the time of impact, a couple D is generated at the clubhead 2 by the shock in the arrow mark direction C2 when the ball 6strikes against the club head 2 advancing toward the arrow markdirection C1 as shown in FIG. 7 and the couple D deforms the shaft 1 inthe arrow mark direction E in such a way that the shaft is crushed.

[0078] At this time, to the filled resilient material 4 are acted both acompressing force applied from the outside by the deformed shaft 1 and acompressing force applied from the inside by the core rod 71 having lessdeformation amount than that of the shaft 1. That is, the resilientmaterial 4 is compressed from both inside and outside, a high repellingforce is generated by this compression, this repelling force restrictsthe deformation of the shaft 1 to a minimum value and at the same timerestricts the vibration of the shaft 1. Accordingly, the energy loss atthe time of impact is reduced, and thereby the repelling force of theshaft 1 at the time of impact is concentrated at the ball 6, so that theinitial speed of the ball and the carry of the ball can be improved bythis preferred embodiment.

[0079] In the preferred embodiment above, although both golf clubs areillustrated as the wood type, they are not limited to this type but theiron type may also be applicable. In the case of the iron type (notshown), a long iron type applied when a certain carry is required is themost preferable one.

[0080] Having described specific examples of the invention withreference to the accompanying drawings, it will be appreciated that thepresent invention is not limited to those precise embodiments, and thatvarious changes and modifications can be effected therein by one ofordinary skill in the art without departing from the scope of theinvention as defined by the appended claims.

What is claimed:
 1. A golf club shaft in which an entire inner region ofa hollow shaft is filled with resilient material having a feature inwhich a rapid application of force causes a high repelling force to beacted on it to be hardly deformed and in turn a gradual application offorce causes the shaft to be easily deformed, wherein a core rod isstored within the shaft along its axis, a lower end of said core rod isfixed to the extremity end of the shaft and the core rod is insertedinto said resilient material.
 2. A golf club shaft according to claim 1in which the core rod and said resilient material is adhered and fixed.3. A golf club shaft according to claim 2 in which an upper end of theresilient material is adhered to and fixed to the shaft.
 4. A golf clubshaft according to claim 1 in which the resilient material is adheredand fixed to the shaft.
 5. A golf club shaft according to claim 2 inwhich the resilient material is adhered and fixed to the shaft.
 6. Agolf club shaft according to claim 1 in which an upper end of theresilient material is adhered to and fixed to the shaft.
 7. A golf clubshaft in the form of a hollow shaft that is at least partially filledwith a resilient material that has a feature in which a rapidapplication of a force at an inner extremity end of the hollow shaftcauses a high repelling to be acted on it and causes it to be hardlydeformed and in turn a gradual application of force at the innerextremity end of the hollow shaft causes the material to be easilydeformed, wherein the range of the extremity end of the hollow shaftwhere the resilient material is filled is from 30 cm to 40 cm from aneck end or from near an end part.
 8. A golf club shaft according toclaim 7 in which a core rod is stored within the shaft along its axis, alower end of said core rod is fixed to the extremity end of the shaftand the core rod is inserted into said resilient material.
 9. A golfclub shaft according to claim 7 in which the core rod and said resilientmaterial is adhered and fixed.
 10. A golf club shaft according to claim8 in which the core rod and said resilient material is adhered andfixed.
 11. A golf club shaft according to claim 7 in which the resilientmaterial is adhered and fixed to the shaft.
 12. A golf club shaftaccording to claim 8 in which the resilient material is adhered andfixed to the shaft.
 13. A golf club shaft according to claim 10 in whichthe resilient material is adhered and fixed to the shaft.
 14. A golfclub shaft according to claim 7 in which an upper end of the resilientmaterial is adhered to and fixed to the shaft.
 15. A golf club shaftaccording to claim 8 in which an upper end of the resilient material isadhered to and fixed to the shaft.
 16. A golf club shaft according toclaim 10 in which an upper end of the resilient material is adhered toand fixed to the shaft.